1. Technical Field of the Invention
The present invention relates to an ultra-precise processing method and apparatus for an inhomogeneous material, which can perform ultra-precise processing even when a workpiece or a tool has low rigidity and an inconstant deformation quantity.
2. Description of the Related Art
FIG. 1A is a type drawing showing a processing step of a large-diameter lightweight mirror for a large reflecting telescope used in the outer space. This large-diameter lightweight mirror 1 includes a thin reflecting plate 2 (for example, a thickness of 3 to 5 mm) supported by a honey-comb body 3 in order to reduce the weight. Although this large-diameter lightweight mirror has a large-diameter of, e.g., 300 to 700 mm, its weight is restricted to less than 150 kg.
Conventionally, when processing and forming a high-precision and mirror-surface-like high-quality (which will be simply referred to as “ultra-precise” hereinafter) reflecting surface on the surface of the above-described large-diameter lightweight mirror, a processing tool 4 (for example, a cylindrical grinding stone) is moved along a predetermined curve (for example, a parabola) by an NC control while rotating the large-diameter lightweight mirror 1 around its center axis Z, thereby processing a reflecting plate 2.
In FIG. 1A, however, the reflecting plate 2 is just partially supported by the honey-comb body 3, and the rigidity of the reflecting plate 2 at a part not supported by the honey-comb body 3 is low. Therefore, during the grinding process using the processing tool, a contact arc length between the processing tool and the reflecting plate 2 (workpiece) largely varies depending on a processing position, and the processing resistance also greatly fluctuates. Therefore, the deformation of the workpiece itself partially differs, and deformation as indicated by a thin line 2′ in FIG. 1B is generated, for example.
As a result, although the processing tool is subjected to precise positional control by the NC control in order to process the workpiece, ultra-precise processing is difficult when the rigidity of the workpiece or the tool is low and its quantity of deformation is inconstant.